Even swans, who are known to mate for life, are unfaithful partners, according to researchers.

Social scientists claim that there is not one culture in which adultery doesn't happen. In the United States, some reports say that one in three married men will cheat at some point; for women, the rate is one in four.

It is a thorny, contentious issue that brings along with it a multitude of questions. Are people born to cheat? Is the seventh commandment still relevant in a country where more than 40 percent of the marriages end in divorce? What constitutes adultery? Is lying worse than cheating?

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To explore all of these questions, "Nightline" went out to the heart of the Bible belt for the fourth installment of the "Nightline Face-Off" series, moderated by co-anchor Cynthia McFadden, asking simply: Are we born to cheat?

It was a packed house. More than 3,000 people -- mostly church members -- showed up to hear the different ideas from the four panelists, all of whom said they are happily married, but who had very different ideas about what constitutes cheating.

God Wants Us to Have the Best Sex

The conversation was a powerful, candid and, at times, painful look at adultery and marriage, and the panel was as complex as the topic.

Pastor Ed Young is a married father of four and senior pastor of the Grapevine, Texas-based Fellowship Church, where the debate took place. Young has written and preached extensively on the topic of marriage and sex, and even has been known to challenge his married congregants to engage in seven days of sex.

"God is pro-sex," Young told "Nightline" prior to the debate. "He thought that up, and He wants us to have the best sex possible. And that is in a marriage -- one man, one woman together. And that's the deal. And I know that a lot of people have slept in the wrong bed. God wants to forgive, but also His ideal is that marriage bed."

Joining Young was Jonathan Daugherty, who identified himself as a recovering sex and porn addict and admitted committing adultery. Daugherty is now back with his wife, with whom he has created the San Antonio-based Be Broken Ministries, where they counsel others suffering from sexual addictions.

"[I] have lived on both sides," he said. "So I hope to be able to put my life on the scale and say this is my experience and this is why I have come to the conclusion I have come to regarding marriage and it's importance."

Daugherty admitted that discussing his personal life in such a public forum is tough.

"You have to bring up some things in the past that were clearly mistakes that I made, and it's not fun to bring those things up," he said. "But I look at it in the sense that if I can help someone who is struggling with those things to come to a conclusion that might improve their life or get the help that they need, then I think it's worth going ahead and putting myself out there and telling people about it."